/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <android_avb/avb_slot_verify.h>
#include <android_avb/avb_chain_partition_descriptor.h>
#include <android_avb/avb_footer.h>
#include <android_avb/avb_hash_descriptor.h>
#include <android_avb/avb_kernel_cmdline_descriptor.h>
#include <android_avb/avb_sha.h>
#include <android_avb/avb_util.h>
#include <android_avb/avb_vbmeta_image.h>
#include <android_avb/avb_version.h>

/* Maximum allow length (in bytes) of a partition name, including
 * ab_suffix.
 */
#define PART_NAME_MAX_SIZE 32

/* Maximum number of partitions that can be loaded with avb_slot_verify(). */
#define MAX_NUMBER_OF_LOADED_PARTITIONS 32

/* Maximum number of vbmeta images that can be loaded with avb_slot_verify(). */
#define MAX_NUMBER_OF_VBMETA_IMAGES 32

/* Maximum size of a vbmeta image - 64 KiB. */
#define VBMETA_MAX_SIZE (64 * 1024)

/* Helper function to see if we should continue with verification in
 * allow_verification_error=true mode if something goes wrong. See the
 * comments for the avb_slot_verify() function for more information.
 */
static inline bool result_should_continue(AvbSlotVerifyResult result)
{
	switch (result) {
	case AVB_SLOT_VERIFY_RESULT_ERROR_OOM:
	case AVB_SLOT_VERIFY_RESULT_ERROR_IO:
	case AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA:
	case AVB_SLOT_VERIFY_RESULT_ERROR_UNSUPPORTED_VERSION:
	case AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_ARGUMENT:
		return false;

	case AVB_SLOT_VERIFY_RESULT_OK:
	case AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION:
	case AVB_SLOT_VERIFY_RESULT_ERROR_ROLLBACK_INDEX:
	case AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED:
		return true;
  }

  return false;
}

static AvbSlotVerifyResult load_and_verify_hash_partition(
    AvbOps* ops,
    const char* const* requested_partitions,
    const char* ab_suffix,
    bool allow_verification_error,
    const AvbDescriptor* descriptor,
    AvbSlotVerifyData* slot_data)
{
	AvbHashDescriptor hash_desc;
	const uint8_t* desc_partition_name = NULL;
	const uint8_t* desc_salt;
	const uint8_t* desc_digest;
	char part_name[PART_NAME_MAX_SIZE];
	AvbSlotVerifyResult ret;
	AvbIOResult io_ret;
	uint8_t* image_buf = NULL;
	size_t part_num_read;
	uint8_t* digest;
	size_t digest_len;
	const char* found;
	uint64_t image_size;

	if (!avb_hash_descriptor_validate_and_byteswap(
		(const AvbHashDescriptor*)descriptor, &hash_desc)) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		goto out;
	}
	desc_partition_name = ((const uint8_t*)descriptor) + sizeof(AvbHashDescriptor);
	desc_salt = desc_partition_name + hash_desc.partition_name_len;
	desc_digest = desc_salt + hash_desc.salt_len;

	if (!avb_validate_utf8(desc_partition_name, hash_desc.partition_name_len)) {
		avb_error("Partition name is not valid UTF-8.\n");
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		goto out;
	}
	/* Don't bother loading or validating unless the partition was
	 * requested in the first place.
	 */
	found = avb_strv_find_str(requested_partitions,
                            (const char*)desc_partition_name,
                            hash_desc.partition_name_len);
	if (found == NULL) {
		ret = AVB_SLOT_VERIFY_RESULT_OK;
		goto out;
	}
	if (!avb_str_concat(part_name,
                      sizeof part_name,
                      (const char*)desc_partition_name,
                      hash_desc.partition_name_len,
                      ab_suffix,
                      avb_strlen(ab_suffix))) {
		avb_error("Partition name and suffix does not fit.\n");
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		goto out;
	}
	/* If we're allowing verification errors then hash_desc.image_size
	 * may no longer match what's in the partition... so in this case
	 * just load the entire partition.
	 *
	 * For example, this can happen if a developer does 'fastboot flash
	 * boot /path/to/new/and/bigger/boot.img'. We want this to work
	 * since it's such a common workflow.
	 */
	image_size = hash_desc.image_size;
	if (0) {
		if (ops->get_size_of_partition == NULL) {
			avb_errorv(part_name,
			": The get_size_of_partition() operation is "
			"not implemented so we may not load the entire partition. "
			"Please implement.",
			NULL);
		} else {
			io_ret = ops->get_size_of_partition(ops, part_name, &image_size);
			if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
				goto out;
			} else if (io_ret != AVB_IO_RESULT_OK) {
				avb_errorv(part_name, ": Error determining partition size.\n", NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
				goto out;
			}
			avb_debugv(part_name, ": Loading entire partition.\n", NULL);
		}
	}
	image_buf = avb_malloc(image_size);
	if (image_buf == NULL) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto out;
	}
	io_ret = ops->read_from_partition(ops, part_name, 0 /* offset */, 
					image_size, image_buf, &part_num_read);
	if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto out;
	} else if (io_ret != AVB_IO_RESULT_OK) {
		avb_errorv(part_name, ": Error loading data from partition.\n", NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
		goto out;
	}
	if (part_num_read != image_size) {
		avb_errorv(part_name, ": Read fewer than requested bytes.\n", NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
		goto out;
	}

	if (avb_strcmp((const char*)hash_desc.hash_algorithm, "sha256") == 0) {
		AvbSHA256Ctx sha256_ctx;
		avb_sha256_init(&sha256_ctx);
		avb_sha256_update(&sha256_ctx, desc_salt, hash_desc.salt_len);
		avb_sha256_update(&sha256_ctx, image_buf, hash_desc.image_size);
		digest = avb_sha256_final(&sha256_ctx);
		digest_len = AVB_SHA256_DIGEST_SIZE;
	} else if (avb_strcmp((const char*)hash_desc.hash_algorithm, "sha512") == 0) {
		AvbSHA512Ctx sha512_ctx;
		avb_sha512_init(&sha512_ctx);
		avb_sha512_update(&sha512_ctx, desc_salt, hash_desc.salt_len);
		avb_sha512_update(&sha512_ctx, image_buf, hash_desc.image_size);
		digest = avb_sha512_final(&sha512_ctx);
		digest_len = AVB_SHA512_DIGEST_SIZE;
	} else {
		avb_errorv(part_name, ": Unsupported hash algorithm.\n", NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		goto out;
	}

	if (digest_len != hash_desc.digest_len) {
		avb_errorv(
			part_name, ": Digest in descriptor not of expected size.\n", NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		goto out;
	}

	if (avb_safe_memcmp(digest, desc_digest, digest_len) != 0) {
		avb_errorv(part_name,
			": Hash of data does not match digest in descriptor.\n",
			NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION;
		goto out;
	}

	ret = AVB_SLOT_VERIFY_RESULT_OK;

out:
	/* If it worked and something was loaded, copy to slot_data. */
	if ((ret == AVB_SLOT_VERIFY_RESULT_OK || result_should_continue(ret)) &&
		image_buf != NULL) {
		AvbPartitionData* loaded_partition;
		if (slot_data->num_loaded_partitions == MAX_NUMBER_OF_LOADED_PARTITIONS) {
			avb_errorv(part_name, ": Too many loaded partitions.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
			goto fail;
		}
		loaded_partition = &slot_data->loaded_partitions[slot_data->num_loaded_partitions++];
		loaded_partition->partition_name = avb_strdup(found);
		loaded_partition->data_size = image_size;
		loaded_partition->data = image_buf;
		image_buf = NULL;
	}

fail:
	if (image_buf != NULL) {
		avb_free(image_buf);
	}
	return ret;
}

static AvbSlotVerifyResult load_requested_partitions(
	AvbOps* ops,
	const char* const* requested_partitions,
	const char* ab_suffix,
	AvbSlotVerifyData* slot_data)
{
	AvbSlotVerifyResult ret;
	uint8_t* image_buf = NULL;
	size_t n;

	if (ops->get_size_of_partition == NULL) {
		avb_error("get_size_of_partition() not implemented.\n");
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_ARGUMENT;
		goto out;
	}

	for (n = 0; requested_partitions[n] != NULL; n++) {
		char part_name[PART_NAME_MAX_SIZE];
		AvbIOResult io_ret;
		uint64_t image_size;
		size_t part_num_read;
		AvbPartitionData* loaded_partition;

		if (!avb_str_concat(part_name,
                        sizeof part_name,
                        requested_partitions[n],
                        avb_strlen(requested_partitions[n]),
                        ab_suffix,
                        avb_strlen(ab_suffix))) {
 			avb_error("Partition name and suffix does not fit.\n");
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
			goto out;
		}

		io_ret = ops->get_size_of_partition(ops, part_name, &image_size);
		if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
			goto out;
		} else if (io_ret != AVB_IO_RESULT_OK) {
			avb_errorv(part_name, ": Error determining partition size.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
			goto out;
		}
		avb_debugv(part_name, ": Loading entire partition.\n", NULL);

		image_buf = avb_malloc(image_size);
		if (image_buf == NULL) {
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
			goto out;
		}

		io_ret = ops->read_from_partition(
		ops, part_name, 0 /* offset */, image_size, image_buf, &part_num_read);
		if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
			goto out;
		} else if (io_ret != AVB_IO_RESULT_OK) {
			avb_errorv(part_name, ": Error loading data from partition.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
			goto out;
		}
		if (part_num_read != image_size) {
			avb_errorv(part_name, ": Read fewer than requested bytes.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
			goto out;
		}

		/* Move to slot_data. */
		if (slot_data->num_loaded_partitions == MAX_NUMBER_OF_LOADED_PARTITIONS) {
			avb_errorv(part_name, ": Too many loaded partitions.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
			goto out;
		}
		loaded_partition =
			&slot_data->loaded_partitions[slot_data->num_loaded_partitions++];
		loaded_partition->partition_name = avb_strdup(requested_partitions[n]);
		if (loaded_partition->partition_name == NULL) {
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
			goto out;
		}
		loaded_partition->data_size = image_size;
		loaded_partition->data = image_buf;
		image_buf = NULL;
	}

	ret = AVB_SLOT_VERIFY_RESULT_OK;

out:
	if (image_buf != NULL) {
		avb_free(image_buf);
	}
	return ret;
}

static AvbSlotVerifyResult load_and_verify_vbmeta
(
	AvbOps* ops,
	const char* const* requested_partitions,
	const char* ab_suffix,
	bool allow_verification_error,
	AvbVBMetaImageFlags toplevel_vbmeta_flags,
	int rollback_index_location,
	const char* partition_name,
	size_t partition_name_len,
	const uint8_t* expected_public_key,
	size_t expected_public_key_length,
	AvbSlotVerifyData* slot_data,
	AvbAlgorithmType* out_algorithm_type)
{
	char full_partition_name[PART_NAME_MAX_SIZE];
	AvbSlotVerifyResult ret;
	AvbIOResult io_ret;
	size_t vbmeta_offset;
	size_t vbmeta_size;
	uint8_t* vbmeta_buf = NULL;
	size_t vbmeta_num_read;
	AvbVBMetaVerifyResult vbmeta_ret;
	const uint8_t* pk_data;
	size_t pk_len;
	AvbVBMetaImageHeader vbmeta_header;
	uint64_t stored_rollback_index;
	const AvbDescriptor** descriptors = NULL;
	size_t num_descriptors;
	size_t n;
	bool is_main_vbmeta;
	bool is_vbmeta_partition;
	AvbVBMetaData* vbmeta_image_data = NULL;

	ret = AVB_SLOT_VERIFY_RESULT_OK;

	avb_assert(slot_data != NULL);

	/* Since we allow top-level vbmeta in 'boot', use
	 * rollback_index_location to determine whether we're the main
	 * vbmeta struct.
	 */
	is_main_vbmeta = (rollback_index_location == 0);
	is_vbmeta_partition = (avb_strcmp(partition_name, "vbmeta") == 0);

	if (!avb_validate_utf8((const uint8_t*)partition_name, partition_name_len)) {
		avb_error("Partition name is not valid UTF-8.\n");
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		goto out;
	}

	/* Construct full partition name. */
	if (!avb_str_concat(full_partition_name,
		sizeof full_partition_name,
		partition_name,
		partition_name_len,
		ab_suffix,
		avb_strlen(ab_suffix))) {
		avb_error("Partition name and suffix does not fit.\n");
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		goto out;
	}

	avb_debugv("Loading vbmeta struct from partition '",
		full_partition_name,
		"'.\n",
		NULL);

	/* If we're loading from the main vbmeta partition, the vbmeta
	 * struct is in the beginning. Otherwise we have to locate it via a
	 * footer.
	 */
	if (is_vbmeta_partition) {
		vbmeta_offset = 0;
		vbmeta_size = VBMETA_MAX_SIZE;
	} else {
		uint8_t footer_buf[AVB_FOOTER_SIZE];
		size_t footer_num_read;
		AvbFooter footer;

		io_ret = ops->read_from_partition(ops,
					full_partition_name,
					-AVB_FOOTER_SIZE,
					AVB_FOOTER_SIZE,
					footer_buf,
					&footer_num_read);
		if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
			goto out;
		} else if (io_ret != AVB_IO_RESULT_OK) {
			avb_errorv(full_partition_name, ": Error loading footer.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
			goto out;
		}
		avb_assert(footer_num_read == AVB_FOOTER_SIZE);

		if (!avb_footer_validate_and_byteswap((const AvbFooter*)footer_buf,&footer)) {
			avb_errorv(full_partition_name, ": Error validating footer.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
			goto out;
		}

		/* Basic footer sanity check since the data is untrusted. */
		if (footer.vbmeta_size > VBMETA_MAX_SIZE) {
			avb_errorv(full_partition_name, ": Invalid vbmeta size in footer.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
			goto out;
		}

		vbmeta_offset = footer.vbmeta_offset;
		vbmeta_size = footer.vbmeta_size;
	}

	vbmeta_buf = avb_malloc(vbmeta_size);
	if (vbmeta_buf == NULL) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto out;
	}
	io_ret = ops->read_from_partition(ops,
					full_partition_name,
					vbmeta_offset,
					vbmeta_size,
					vbmeta_buf,
					&vbmeta_num_read);
	if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto out;
	} else if (io_ret != AVB_IO_RESULT_OK) {
		/* If we're looking for 'vbmeta' but there is no such partition,
		* go try to get it from the boot partition instead.
		*/
		if (is_main_vbmeta && io_ret == AVB_IO_RESULT_ERROR_NO_SUCH_PARTITION && is_vbmeta_partition) {
			avb_debugv(full_partition_name,
			": No such partition. Trying 'boot' instead.\n",
			NULL);
			ret = load_and_verify_vbmeta(ops,
					requested_partitions,
					ab_suffix,
					allow_verification_error,
					0 /* toplevel_vbmeta_flags */,
					0 /* rollback_index_location */,
					"boot",
					avb_strlen("boot"),
					NULL /* expected_public_key */,
					0 /* expected_public_key_length */,
					slot_data,
					out_algorithm_type);
			goto out;
		} else {
			avb_errorv(full_partition_name, ": Error loading vbmeta data.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
			goto out;
		}
	}
	avb_assert(vbmeta_num_read <= vbmeta_size);
	/* Check if the image is properly signed and get the public key used
	 * to sign the image.
	 */
	vbmeta_ret = avb_vbmeta_image_verify(vbmeta_buf, vbmeta_num_read, &pk_data, &pk_len);
	switch (vbmeta_ret) {
	case AVB_VBMETA_VERIFY_RESULT_OK:
		avb_assert(pk_data != NULL && pk_len > 0);
		break;

	case AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED:
	case AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH:
	case AVB_VBMETA_VERIFY_RESULT_SIGNATURE_MISMATCH:
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION;
		avb_errorv(full_partition_name,
			": Error verifying vbmeta image: ",
			avb_vbmeta_verify_result_to_string(vbmeta_ret),
			"\n",
			NULL);
		if (!allow_verification_error) {
			goto out;
		}
		break;

	case AVB_VBMETA_VERIFY_RESULT_INVALID_VBMETA_HEADER:
		/* No way to continue this case. */
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		avb_errorv(full_partition_name,
			": Error verifying vbmeta image: invalid vbmeta header\n",
			NULL);
		goto out;

	case AVB_VBMETA_VERIFY_RESULT_UNSUPPORTED_VERSION:
		/* No way to continue this case. */
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_UNSUPPORTED_VERSION;
		avb_errorv(full_partition_name,
			": Error verifying vbmeta image: unsupported AVB version\n",
			NULL);
		goto out;
	}

	/* Byteswap the header. */
	avb_vbmeta_image_header_to_host_byte_order((AvbVBMetaImageHeader*)vbmeta_buf,
                                             &vbmeta_header);

	/* If we're the toplevel, assign flags so they'll be passed down. */
	if (is_main_vbmeta) {
		toplevel_vbmeta_flags = (AvbVBMetaImageFlags)vbmeta_header.flags;
	} else {
		if (vbmeta_header.flags != 0) {
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
			avb_errorv(full_partition_name,
				": chained vbmeta image has non-zero flags\n",
				NULL);
			goto out;
		}
	}

	/* Check if key used to make signature matches what is expected. */
	if (pk_data != NULL) {
		if (expected_public_key != NULL) {
			avb_assert(!is_main_vbmeta);
			if (expected_public_key_length != pk_len ||
			avb_safe_memcmp(expected_public_key, pk_data, pk_len) != 0) {
				avb_errorv(full_partition_name,
					": Public key used to sign data does not match key in chain "
					"partition descriptor.\n",
					NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED;
				if (!allow_verification_error) {
					goto out;
				}
			}
		} else {
			bool key_is_trusted = false;
			const uint8_t* pk_metadata = NULL;
			size_t pk_metadata_len = 0;

			if (vbmeta_header.public_key_metadata_size > 0) {
				pk_metadata = vbmeta_buf + sizeof(AvbVBMetaImageHeader) +
				vbmeta_header.authentication_data_block_size +
				vbmeta_header.public_key_metadata_offset;
				pk_metadata_len = vbmeta_header.public_key_metadata_size;
			}

			avb_assert(is_main_vbmeta);
			io_ret = ops->validate_vbmeta_public_key(
				ops, pk_data, pk_len, pk_metadata, pk_metadata_len, &key_is_trusted);
			if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
				goto out;
			} else if (io_ret != AVB_IO_RESULT_OK) {
				avb_errorv(full_partition_name,
				": Error while checking public key used to sign data.\n",
				NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
				goto out;
			}
			if (!key_is_trusted) {
				avb_errorv(full_partition_name,
				": Public key used to sign data rejected.\n",
				NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED;
				if (!allow_verification_error) {
					goto out;
				}
			}
		}
	}

	/* Check rollback index. */
	io_ret = ops->read_rollback_index(
		ops, rollback_index_location, &stored_rollback_index);
	if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto out;
	} else if (io_ret != AVB_IO_RESULT_OK) {
		avb_errorv(full_partition_name,
			": Error getting rollback index for location.\n",
			NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
		goto out;
	}
	if (vbmeta_header.rollback_index < stored_rollback_index) {
		avb_errorv(
			full_partition_name,
			": Image rollback index is less than the stored rollback index.\n",
			NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_ROLLBACK_INDEX;
		if (!allow_verification_error) {
			goto out;
		}
	}

	/* Copy vbmeta to vbmeta_images before recursing. */
	if (is_main_vbmeta) {
		avb_assert(slot_data->num_vbmeta_images == 0);
	} else {
		avb_assert(slot_data->num_vbmeta_images > 0);
	}
	if (slot_data->num_vbmeta_images == MAX_NUMBER_OF_VBMETA_IMAGES) {
		avb_errorv(full_partition_name, ": Too many vbmeta images.\n", NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto out;
	}
	vbmeta_image_data = &slot_data->vbmeta_images[slot_data->num_vbmeta_images++];
	vbmeta_image_data->partition_name = avb_strdup(partition_name);
	vbmeta_image_data->vbmeta_data = vbmeta_buf;
	/* Note that |vbmeta_buf| is actually |vbmeta_num_read| bytes long
	 * and this includes data past the end of the image. Pass the
	 * actual size of the vbmeta image. Also, no need to use
	 * avb_safe_add() since the header has already been verified.
	 */
	vbmeta_image_data->vbmeta_size =
	sizeof(AvbVBMetaImageHeader) +
	vbmeta_header.authentication_data_block_size +
	vbmeta_header.auxiliary_data_block_size;
	vbmeta_image_data->verify_result = vbmeta_ret;
  /* If verification has been disabled by setting a bit in the image,
   * we're done... except that we need to load the entirety of the
   * requested partitions.
   */
  if (vbmeta_header.flags & AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED) {
    AvbSlotVerifyResult sub_ret;
    avb_debugv(
        full_partition_name, ": VERIFICATION_DISABLED bit is set.\n", NULL);
    /* If load_requested_partitions() fail it is always a fatal
     * failure (e.g. ERROR_INVALID_ARGUMENT, ERROR_OOM, etc.) rather
     * than recoverable (e.g. one where result_should_continue()
     * returns true) and we want to convey that error.
     */
    sub_ret = load_requested_partitions(
        ops, requested_partitions, ab_suffix, slot_data);
    if (sub_ret != AVB_SLOT_VERIFY_RESULT_OK) {
      ret = sub_ret;
    }
    goto out;
  }
	/* Now go through all descriptors and take the appropriate action:
	 *
	 * - hash descriptor: Load data from partition, calculate hash, and
	 *   checks that it matches what's in the hash descriptor.
	 *
	 * - hashtree descriptor: Do nothing since verification happens
	 *   on-the-fly from within the OS.
	 *
	 * - chained partition descriptor: Load the footer, load the vbmeta
	 *   image, verify vbmeta image (includes rollback checks, hash
	 *   checks, bail on chained partitions).
	 */
	descriptors =
	avb_descriptor_get_all(vbmeta_buf, vbmeta_num_read, &num_descriptors);
	for (n = 0; n < num_descriptors; n++) {
		AvbDescriptor desc;

		if (!avb_descriptor_validate_and_byteswap(descriptors[n], &desc)) {
			avb_errorv(full_partition_name, ": Descriptor is invalid.\n", NULL);
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
			goto out;
		}

		switch (desc.tag) {
		case AVB_DESCRIPTOR_TAG_HASH: {
			AvbSlotVerifyResult sub_ret;
			sub_ret = load_and_verify_hash_partition(ops,
                                                 requested_partitions,
                                                 ab_suffix,
                                                 allow_verification_error,
                                                 descriptors[n],
                                                 slot_data);
			if (sub_ret != AVB_SLOT_VERIFY_RESULT_OK) {
				ret = sub_ret;
				if (!allow_verification_error || !result_should_continue(ret)) {
					goto out;
				}
			}
		} break;

		case AVB_DESCRIPTOR_TAG_CHAIN_PARTITION: {
			AvbSlotVerifyResult sub_ret;
			AvbChainPartitionDescriptor chain_desc;
			const uint8_t* chain_partition_name;
			const uint8_t* chain_public_key;

			/* Only allow CHAIN_PARTITION descriptors in the main vbmeta image. */
			if (!is_main_vbmeta) {
				avb_errorv(full_partition_name,
                     			": Encountered chain descriptor not in main image.\n",
                     			NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
				goto out;
			}

			if (!avb_chain_partition_descriptor_validate_and_byteswap(
				(AvbChainPartitionDescriptor*)descriptors[n], &chain_desc)) {
				avb_errorv(full_partition_name,
                    			 ": Chain partition descriptor is invalid.\n",
                    			 NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
				goto out;
			}

			if (chain_desc.rollback_index_location == 0) {
				avb_errorv(full_partition_name,
                     			": Chain partition has invalid "
                     			"rollback_index_location field.\n",
                    			 NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
				goto out;
			}

			chain_partition_name = ((const uint8_t*)descriptors[n]) +
                               sizeof(AvbChainPartitionDescriptor);
			chain_public_key = chain_partition_name + chain_desc.partition_name_len;

			sub_ret = load_and_verify_vbmeta(ops,
                                         requested_partitions,
                                         ab_suffix,
                                         allow_verification_error,
                                         toplevel_vbmeta_flags,
                                         chain_desc.rollback_index_location,
                                         (const char*)chain_partition_name,
                                         chain_desc.partition_name_len,
                                         chain_public_key,
                                         chain_desc.public_key_len,
                                         slot_data,
                                         NULL /* out_algorithm_type */);
			if (sub_ret != AVB_SLOT_VERIFY_RESULT_OK) {
				ret = sub_ret;
				if (!result_should_continue(ret)) {
					goto out;
				}
			}
		} break;

		case AVB_DESCRIPTOR_TAG_KERNEL_CMDLINE: {
			const uint8_t* kernel_cmdline;
			AvbKernelCmdlineDescriptor kernel_cmdline_desc;
			bool apply_cmdline;

			if (!avb_kernel_cmdline_descriptor_validate_and_byteswap(
				(AvbKernelCmdlineDescriptor*)descriptors[n],
				&kernel_cmdline_desc)) {
				avb_errorv(full_partition_name,
                     			": Kernel cmdline descriptor is invalid.\n",
                     			NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
				goto out;
			}

			kernel_cmdline = ((const uint8_t*)descriptors[n]) +
				sizeof(AvbKernelCmdlineDescriptor);

			if (!avb_validate_utf8(kernel_cmdline,
                               kernel_cmdline_desc.kernel_cmdline_length)) {
				avb_errorv(full_partition_name,
                     			": Kernel cmdline is not valid UTF-8.\n",
                     			NULL);
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
				goto out;
			}

			/* Compare the flags for top-level VBMeta struct with flags in
			 * the command-line descriptor so command-line snippets only
			 * intended for a certain mode (dm-verity enabled/disabled)
			 * are skipped if applicable.
			 */
			apply_cmdline = true;
			if (toplevel_vbmeta_flags & AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED) {
				if (kernel_cmdline_desc.flags &
  					AVB_KERNEL_CMDLINE_FLAGS_USE_ONLY_IF_HASHTREE_NOT_DISABLED) {
					apply_cmdline = false;
				}
			} else {
				if (kernel_cmdline_desc.flags &
					AVB_KERNEL_CMDLINE_FLAGS_USE_ONLY_IF_HASHTREE_DISABLED) {
					apply_cmdline = false;
				}
			}

			if (apply_cmdline) {
				if (slot_data->cmdline == NULL) {
					slot_data->cmdline =
					avb_calloc(kernel_cmdline_desc.kernel_cmdline_length + 1);
					if (slot_data->cmdline == NULL) {
						ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
						goto out;
					}
					avb_memcpy(slot_data->cmdline,
                       				kernel_cmdline,
                       				kernel_cmdline_desc.kernel_cmdline_length);
					} else {
					/* new cmdline is: <existing_cmdline> + ' ' + <newcmdline> + '\0' */
					size_t orig_size = avb_strlen(slot_data->cmdline);
					size_t new_size =
                				orig_size + 1 + kernel_cmdline_desc.kernel_cmdline_length + 1;
					char* new_cmdline = avb_calloc(new_size);
					if (new_cmdline == NULL) {
						ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
						goto out;
					}
					avb_memcpy(new_cmdline, slot_data->cmdline, orig_size);
					new_cmdline[orig_size] = ' ';
					avb_memcpy(new_cmdline + orig_size + 1,
 					kernel_cmdline,
					kernel_cmdline_desc.kernel_cmdline_length);
					avb_free(slot_data->cmdline);
					slot_data->cmdline = new_cmdline;
				}
			}
		} break;

		/* Explicit fall-through */
		case AVB_DESCRIPTOR_TAG_PROPERTY:
		case AVB_DESCRIPTOR_TAG_HASHTREE:
		/* Do nothing. */
		break;
		}
	}

	if (rollback_index_location >= AVB_MAX_NUMBER_OF_ROLLBACK_INDEX_LOCATIONS) {
		avb_errorv(
		full_partition_name, ": Invalid rollback_index_location.\n", NULL);
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
		goto out;
	}

	slot_data->rollback_indexes[rollback_index_location] =
		vbmeta_header.rollback_index;

	if (out_algorithm_type != NULL) {
		*out_algorithm_type = (AvbAlgorithmType)vbmeta_header.algorithm_type;
	}

out:
	/* If |vbmeta_image_data| isn't NULL it means that it adopted
	 * |vbmeta_buf| so in that case don't free it here.
	 */
	if (vbmeta_image_data == NULL) {
		if (vbmeta_buf != NULL) {
			avb_free(vbmeta_buf);
		}
	}
	if (descriptors != NULL) {
		avb_free(descriptors);
	}
	return ret;
}

#define NUM_GUIDS 3

/* Substitutes all variables (e.g. $(ANDROID_SYSTEM_PARTUUID)) with
 * values. Returns NULL on OOM, otherwise the cmdline with values
 * replaced.
 */
static char* sub_cmdline(AvbOps* ops,
                         const char* cmdline,
                         const char* ab_suffix,
                         bool using_boot_for_vbmeta)
{
	const char* part_name_str[NUM_GUIDS] = {"system", "boot", "vbmeta"};
	const char* replace_str[NUM_GUIDS] = {"$(ANDROID_SYSTEM_PARTUUID)",
                                        "$(ANDROID_BOOT_PARTUUID)",
                                        "$(ANDROID_VBMETA_PARTUUID)"};
	char* ret = NULL;
	AvbIOResult io_ret;
	size_t n;

	/* Special-case for when the top-level vbmeta struct is in the boot
	 * partition.
	 */
	if (using_boot_for_vbmeta) {
		part_name_str[2] = "boot";
	}

	/* Replace unique partition GUIDs */
	for (n = 0; n < NUM_GUIDS; n++) {
		char part_name[PART_NAME_MAX_SIZE];
		char guid_buf[37];

		if (!avb_str_concat(part_name,
                        	sizeof part_name,
                        	part_name_str[n],
                        	avb_strlen(part_name_str[n]),
                        	ab_suffix,
                        	avb_strlen(ab_suffix))) {
			avb_error("Partition name and suffix does not fit.\n");
			goto fail;
		}

		io_ret = ops->get_unique_guid_for_partition(
			ops, part_name, guid_buf, sizeof guid_buf);
		if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
			return NULL;
		} else if (io_ret != AVB_IO_RESULT_OK) {
			avb_error("Error getting unique GUID for partition.\n");
			goto fail;
		}

		if (ret == NULL) {
			ret = avb_replace(cmdline, replace_str[n], guid_buf);
		} else {
			char* new_ret = avb_replace(ret, replace_str[n], guid_buf);
			avb_free(ret);
 			ret = new_ret;
		}
		if (ret == NULL) {
			goto fail;
		}
	}

	return ret;

fail:
	if (ret != NULL) {
		avb_free(ret);
	}
	return NULL;
}

static int cmdline_append_option(AvbSlotVerifyData* slot_data,
                                 const char* key,
                                 const char* value)
{
	size_t offset, key_len, value_len;
	char* new_cmdline;

	key_len = avb_strlen(key);
	value_len = avb_strlen(value);

	offset = 0;
	if (slot_data->cmdline != NULL) {
		offset = avb_strlen(slot_data->cmdline);
		if (offset > 0) {
			offset += 1;
		}
	}

	new_cmdline = avb_calloc(offset + key_len + value_len + 2);
	if (new_cmdline == NULL) {
		return 0;
	}
	if (offset > 0) {
		avb_memcpy(new_cmdline, slot_data->cmdline, offset - 1);
		new_cmdline[offset - 1] = ' ';
	}
	avb_memcpy(new_cmdline + offset, key, key_len);
	new_cmdline[offset + key_len] = '=';
	avb_memcpy(new_cmdline + offset + key_len + 1, value, value_len);
	if (slot_data->cmdline != NULL) {
		avb_free(slot_data->cmdline);
	}
	slot_data->cmdline = new_cmdline;

	return 1;
}

#define AVB_MAX_DIGITS_UINT64 32

/* Writes |value| to |digits| in base 10 followed by a NUL byte.
 * Returns number of characters written excluding the NUL byte.
 */
static size_t uint64_to_base10(uint64_t value,
                               char digits[AVB_MAX_DIGITS_UINT64])
{
	char rev_digits[AVB_MAX_DIGITS_UINT64];
	size_t n, num_digits;

	for (num_digits = 0; num_digits < AVB_MAX_DIGITS_UINT64 - 1;) {
		rev_digits[num_digits++] = (value % 10) + '0';
		value /= 10;
		if (value == 0) {
			break;
		}
	}

	for (n = 0; n < num_digits; n++) {
		digits[n] = rev_digits[num_digits - 1 - n];
	}
	digits[n] = '\0';
	return n;
}

static int cmdline_append_version(AvbSlotVerifyData* slot_data,
                                  const char* key,
                                  uint64_t major_version,
                                  uint64_t minor_version)
{
	char major_digits[AVB_MAX_DIGITS_UINT64];
	char minor_digits[AVB_MAX_DIGITS_UINT64];
	char combined[AVB_MAX_DIGITS_UINT64 * 2 + 1];
	size_t num_major_digits, num_minor_digits;

	num_major_digits = uint64_to_base10(major_version, major_digits);
	num_minor_digits = uint64_to_base10(minor_version, minor_digits);
	avb_memcpy(combined, major_digits, num_major_digits);
	combined[num_major_digits] = '.';
	avb_memcpy(combined + num_major_digits + 1, minor_digits, num_minor_digits);
	combined[num_major_digits + 1 + num_minor_digits] = '\0';

	return cmdline_append_option(slot_data, key, combined);
}

static int cmdline_append_uint64_base10(AvbSlotVerifyData* slot_data,
                                        const char* key,
                                        uint64_t value)
{
	char digits[AVB_MAX_DIGITS_UINT64];
	uint64_to_base10(value, digits);
	return cmdline_append_option(slot_data, key, digits);
}

static int cmdline_append_hex(AvbSlotVerifyData* slot_data,
                              const char* key,
                              const uint8_t* data,
                              size_t data_len)
{
	char hex_digits[17] = "0123456789abcdef";
	char* hex_data;
	int ret;
	size_t n;

	hex_data = avb_malloc(data_len * 2 + 1);
	if (hex_data == NULL) {
		return 0;
	}

	for (n = 0; n < data_len; n++) {
		hex_data[n * 2] = hex_digits[data[n] >> 4];
		hex_data[n * 2 + 1] = hex_digits[data[n] & 0x0f];
	}
	hex_data[n * 2] = '\0';

	ret = cmdline_append_option(slot_data, key, hex_data);
	avb_free(hex_data);
	return ret;
}

static AvbSlotVerifyResult append_options(
    AvbOps* ops,
    AvbSlotVerifyData* slot_data,
    AvbVBMetaImageHeader* toplevel_vbmeta,
    AvbAlgorithmType algorithm_type,
    AvbHashtreeErrorMode hashtree_error_mode) {
  AvbSlotVerifyResult ret;
  const char* verity_mode = NULL;
  bool is_device_unlocked;
  AvbIOResult io_ret;

  /* Add androidboot.vbmeta.device option. */
  if (!cmdline_append_option(slot_data,
                             "androidboot.vbmeta.device",
                             "PARTUUID=$(ANDROID_VBMETA_PARTUUID)")) {
    ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
    goto out;
  }

  /* Add androidboot.vbmeta.avb_version option. */
  if (!cmdline_append_version(slot_data,
                              "androidboot.vbmeta.avb_version",
                              AVB_VERSION_MAJOR,
                              AVB_VERSION_MINOR)) {
    ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
    goto out;
  }

  /* Set androidboot.avb.device_state to "locked" or "unlocked". */
  io_ret = ops->read_is_device_unlocked(ops, &is_device_unlocked);
  if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
    ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
    goto out;
  } else if (io_ret != AVB_IO_RESULT_OK) {
    avb_error("Error getting device state.\n");
    ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
    goto out;
  }
  if (!cmdline_append_option(slot_data,
                             "androidboot.vbmeta.device_state",
                             is_device_unlocked ? "unlocked" : "locked")) {
    ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
    goto out;
  }

  /* Set androidboot.vbmeta.{hash_alg, size, digest} - use same hash
   * function as is used to sign vbmeta.
   */
  switch (algorithm_type) {
    /* Explicit fallthrough. */
    case AVB_ALGORITHM_TYPE_NONE:
    case AVB_ALGORITHM_TYPE_SHA256_RSA2048:
    case AVB_ALGORITHM_TYPE_SHA256_RSA4096:
    case AVB_ALGORITHM_TYPE_SHA256_RSA8192: {
      AvbSHA256Ctx ctx;
      size_t n, total_size = 0;
      avb_sha256_init(&ctx);
      for (n = 0; n < slot_data->num_vbmeta_images; n++) {
        avb_sha256_update(&ctx,
                          slot_data->vbmeta_images[n].vbmeta_data,
                          slot_data->vbmeta_images[n].vbmeta_size);
        total_size += slot_data->vbmeta_images[n].vbmeta_size;
      }
      if (!cmdline_append_option(
              slot_data, "androidboot.vbmeta.hash_alg", "sha256") ||
          !cmdline_append_uint64_base10(
              slot_data, "androidboot.vbmeta.size", total_size) ||
          !cmdline_append_hex(slot_data,
                              "androidboot.vbmeta.digest",
                              avb_sha256_final(&ctx),
                              AVB_SHA256_DIGEST_SIZE)) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto out;
      }
    } break;
    /* Explicit fallthrough. */
    case AVB_ALGORITHM_TYPE_SHA512_RSA2048:
    case AVB_ALGORITHM_TYPE_SHA512_RSA4096:
    case AVB_ALGORITHM_TYPE_SHA512_RSA8192: {
      AvbSHA512Ctx ctx;
      size_t n, total_size = 0;
      avb_sha512_init(&ctx);
      for (n = 0; n < slot_data->num_vbmeta_images; n++) {
        avb_sha512_update(&ctx,
                          slot_data->vbmeta_images[n].vbmeta_data,
                          slot_data->vbmeta_images[n].vbmeta_size);
        total_size += slot_data->vbmeta_images[n].vbmeta_size;
      }
      if (!cmdline_append_option(
              slot_data, "androidboot.vbmeta.hash_alg", "sha512") ||
          !cmdline_append_uint64_base10(
              slot_data, "androidboot.vbmeta.size", total_size) ||
          !cmdline_append_hex(slot_data,
                              "androidboot.vbmeta.digest",
                              avb_sha512_final(&ctx),
                              AVB_SHA512_DIGEST_SIZE)) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto out;
      }
    } break;
    case _AVB_ALGORITHM_NUM_TYPES:
      avb_assert_not_reached();
      break;
  }

  /* Set androidboot.veritymode and androidboot.vbmeta.invalidate_on_error */
  if (toplevel_vbmeta->flags & AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED) {
    verity_mode = "disabled";
  } else {
    const char* dm_verity_mode = NULL;
    char* new_ret;

    switch (hashtree_error_mode) {
      case AVB_HASHTREE_ERROR_MODE_RESTART_AND_INVALIDATE:
        if (!cmdline_append_option(
                slot_data, "androidboot.vbmeta.invalidate_on_error", "yes")) {
          ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
          goto out;
        }
        verity_mode = "enforcing";
        dm_verity_mode = "restart_on_corruption";
        break;
      case AVB_HASHTREE_ERROR_MODE_RESTART:
        verity_mode = "enforcing";
        dm_verity_mode = "restart_on_corruption";
        break;
      case AVB_HASHTREE_ERROR_MODE_EIO:
        verity_mode = "eio";
        /* For now there's no option to specify the EIO mode. So
         * just use 'ignore_zero_blocks' since that's already set
         * and dm-verity-target.c supports specifying this multiple
         * times.
         */
        dm_verity_mode = "ignore_zero_blocks";
        break;
      case AVB_HASHTREE_ERROR_MODE_LOGGING:
        verity_mode = "logging";
        dm_verity_mode = "ignore_corruption";
        break;
    }
    new_ret = avb_replace(
        slot_data->cmdline, "$(ANDROID_VERITY_MODE)", dm_verity_mode);
    avb_free(slot_data->cmdline);
    slot_data->cmdline = new_ret;
    if (slot_data->cmdline == NULL) {
      ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
      goto out;
    }
  }
  if (!cmdline_append_option(
          slot_data, "androidboot.veritymode", verity_mode)) {
    ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
    goto out;
  }

  ret = AVB_SLOT_VERIFY_RESULT_OK;

out:

  return ret;
}

AvbSlotVerifyResult avb_slot_verify(AvbOps* ops,
                                    const char* const* requested_partitions,
                                    const char* ab_suffix,
                                    AvbSlotVerifyFlags flags,
                                    AvbHashtreeErrorMode hashtree_error_mode,
                                    AvbSlotVerifyData** out_data)
{
	AvbSlotVerifyResult ret;
	AvbSlotVerifyData* slot_data = NULL;
	AvbAlgorithmType algorithm_type = AVB_ALGORITHM_TYPE_SHA256_RSA4096;
	bool using_boot_for_vbmeta = false;
	AvbVBMetaImageHeader toplevel_vbmeta;
	bool allow_verification_error =
		(flags & AVB_SLOT_VERIFY_FLAGS_ALLOW_VERIFICATION_ERROR);

	/* Fail early if we're missing the AvbOps needed for slot verification.
	 *
	 * For now, handle get_size_of_partition() not being implemented. In
	 * a later release we may change that.
	 */
	avb_assert(ops->read_is_device_unlocked != NULL);
	avb_assert(ops->read_from_partition != NULL);
	avb_assert(ops->validate_vbmeta_public_key != NULL);
	avb_assert(ops->read_rollback_index != NULL);
	avb_assert(ops->get_unique_guid_for_partition != NULL);
	/* avb_assert(ops->get_size_of_partition != NULL); */

	if (out_data != NULL) {
		*out_data = NULL;
	}

	/* Allowing dm-verity errors defeats the purpose of verified boot so
	 * only allow this if set up to allow verification errors
	 * (e.g. typically only UNLOCKED mode).
	 */
	if (hashtree_error_mode == AVB_HASHTREE_ERROR_MODE_LOGGING &&
		!allow_verification_error) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_ARGUMENT;
		goto fail;
	}

	slot_data = avb_calloc(sizeof(AvbSlotVerifyData));
	if (slot_data == NULL) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto fail;
	}
	slot_data->vbmeta_images =
		avb_calloc(sizeof(AvbVBMetaData) * MAX_NUMBER_OF_VBMETA_IMAGES);
	if (slot_data->vbmeta_images == NULL) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto fail;
	}
	slot_data->loaded_partitions =
		avb_calloc(sizeof(AvbPartitionData) * MAX_NUMBER_OF_LOADED_PARTITIONS);
	if (slot_data->loaded_partitions == NULL) {
		ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
		goto fail;
	}

	ret = load_and_verify_vbmeta(ops,
                               requested_partitions,
                               ab_suffix,
                               allow_verification_error,
                               0 /* toplevel_vbmeta_flags */,
                               0 /* rollback_index_location */,
                               "vbmeta",
                               avb_strlen("vbmeta"),
                               NULL /* expected_public_key */,
                               0 /* expected_public_key_length */,
                               slot_data,
                               &algorithm_type);
	if (!allow_verification_error && ret != AVB_SLOT_VERIFY_RESULT_OK) {
		goto fail;
	}

	/* If things check out, mangle the kernel command-line as needed. */
	if (result_should_continue(ret)) {
		if (avb_strcmp(slot_data->vbmeta_images[0].partition_name, "vbmeta") != 0) {
		avb_assert(
  			avb_strcmp(slot_data->vbmeta_images[0].partition_name, "boot") == 0);
			using_boot_for_vbmeta = true;
		}

		/* Byteswap top-level vbmeta header since we'll need it below. */
		avb_vbmeta_image_header_to_host_byte_order(
        		(const AvbVBMetaImageHeader*)slot_data->vbmeta_images[0].vbmeta_data,
        		&toplevel_vbmeta);

		/* Fill in |ab_suffix| field. */
		slot_data->ab_suffix = avb_strdup(ab_suffix);
		if (slot_data->ab_suffix == NULL) {
			ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
			goto fail;
		}

    /* If verification is disabled, we are done ... we specifically
     * don't want to add any androidboot.* options since verification
     * is disabled.
     */
    if (toplevel_vbmeta.flags & AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED) {
      /* Since verification is disabled we didn't process any
       * descriptors and thus there's no cmdline... so set root= such
       * that the system partition is mounted.
       */
      avb_assert(slot_data->cmdline == NULL);
      slot_data->cmdline =
          avb_strdup("root=PARTUUID=$(ANDROID_SYSTEM_PARTUUID)");
      if (slot_data->cmdline == NULL) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto fail;
      }
    } else {
      /* Add options - any failure in append_options() is either an
       * I/O or OOM error.
       */
      AvbSlotVerifyResult sub_ret = append_options(ops,
                                                   slot_data,
                                                   &toplevel_vbmeta,
                                                   algorithm_type,
                                                   hashtree_error_mode);
      if (sub_ret != AVB_SLOT_VERIFY_RESULT_OK) {
        ret = sub_ret;
        goto fail;
      }
    }

		/* Substitute $(ANDROID_SYSTEM_PARTUUID) and friends. */
		if (slot_data->cmdline != NULL) {
			char* new_cmdline;
			new_cmdline = sub_cmdline(
			ops, slot_data->cmdline, ab_suffix, using_boot_for_vbmeta);
			if (new_cmdline == NULL) {
				ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
				goto fail;
			}
			avb_free(slot_data->cmdline);
			slot_data->cmdline = new_cmdline;
		}

		if (out_data != NULL) {
			*out_data = slot_data;
		} else {
			avb_slot_verify_data_free(slot_data);
		}
	}

	if (!allow_verification_error) {
		avb_assert(ret == AVB_SLOT_VERIFY_RESULT_OK);
	}

	return ret;

fail:
	if (slot_data != NULL) {
		avb_slot_verify_data_free(slot_data);
	}
	return ret;
}

void avb_slot_verify_data_free(AvbSlotVerifyData* data)
{
	if (data->ab_suffix != NULL) {
		avb_free(data->ab_suffix);
	}
	if (data->cmdline != NULL) {
		avb_free(data->cmdline);
	}
	if (data->vbmeta_images != NULL) {
		size_t n;
		for (n = 0; n < data->num_vbmeta_images; n++) {
			AvbVBMetaData* vbmeta_image = &data->vbmeta_images[n];
			if (vbmeta_image->partition_name != NULL) {
				avb_free(vbmeta_image->partition_name);
			}
			if (vbmeta_image->vbmeta_data != NULL) {
				avb_free(vbmeta_image->vbmeta_data);
			}
		}
		avb_free(data->vbmeta_images);
	}
	if (data->loaded_partitions != NULL) {
		size_t n;
		for (n = 0; n < data->num_loaded_partitions; n++) {
			AvbPartitionData* loaded_partition = &data->loaded_partitions[n];
			if (loaded_partition->partition_name != NULL) {
				avb_free(loaded_partition->partition_name);
			}
			if (loaded_partition->data != NULL) {
				avb_free(loaded_partition->data);
			}
		}
		avb_free(data->loaded_partitions);
	}
	avb_free(data);
}

const char* avb_slot_verify_result_to_string(AvbSlotVerifyResult result)
{
	const char* ret = NULL;

	switch (result) {
	case AVB_SLOT_VERIFY_RESULT_OK:
		ret = "OK";
		break;
	case AVB_SLOT_VERIFY_RESULT_ERROR_OOM:
		ret = "ERROR_OOM";
 		break;
	case AVB_SLOT_VERIFY_RESULT_ERROR_IO:
		ret = "ERROR_IO";
		break;
	case AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION:
		ret = "ERROR_VERIFICATION";
		break;
	case AVB_SLOT_VERIFY_RESULT_ERROR_ROLLBACK_INDEX:
		ret = "ERROR_ROLLBACK_INDEX";
		break;
	case AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED:
		ret = "ERROR_PUBLIC_KEY_REJECTED";
		break;
	case AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA:
		ret = "ERROR_INVALID_METADATA";
		break;
	case AVB_SLOT_VERIFY_RESULT_ERROR_UNSUPPORTED_VERSION:
		ret = "ERROR_UNSUPPORTED_VERSION";
		break;
	case AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_ARGUMENT:
		ret = "ERROR_INVALID_ARGUMENT";
		break;
	/* Do not add a 'default:' case here because of -Wswitch. */
	}

	if (ret == NULL) {
		avb_error("Unknown AvbSlotVerifyResult value.\n");
		ret = "(unknown)";
	}

	return ret;
}
